1. Field of the Invention
The present invention relates to the fabrication of a semiconductor laser device, and in particular to the formation of a metal contact forming part of the semiconductor laser device.
2. The Background Art
Semiconductor laser devices are widely available. One type of semiconductor laser device is tuneable around the 1.5 μm wavelength for use in DWDM optical communications. Such semiconductor laser devices may be based on an InP semiconductor system.
One way of forming a p-metal contact on an InP semiconductor system is to deposit a lattice-matched InGaAs layer, followed by the deposition of layers of Titanium (Ti), Platinum (Pt) and Gold (Au) to form a so-called non-alloyed ohmic contact. The Au layer forms a contact pad, while the Pt layer acts as a barrier to inhibit diffusion of gold into the semiconductor structure. The article “Au/Pt/Ti contacts to p-In0.53Ga0.47As and n-InP layers formed by a single metallization common step and rapid thermal processing” by A. Katz et al, J. Appl. Phys. 68 (3), 1 Aug. 1990, the whole contents of which are hereby incorporated by reference, discusses the formation of such a contact by evaporating the Au bonding layer during a single deposition process with the Ti and Pt layers, followed by rapid thermal processing.
Sudden failure is a problem which can afflict semiconductor laser devices. One cause of such sudden failure is Au migration into the InP material, particularly as Au migrates rapidly in InP material.